During manufacturing of a semiconductor device, the device is usually processed at many work stations or processing machines. The transporting or conveying of a partially finished device, or a work-in-process (WIP) part, e.g. a semiconductor wafer, is an important aspect in the total manufacturing process. A semiconductor wafer must be stored or transported between various process stations in order to perform various fabrication processes.
Multiple wafers are typically stored and transported together in wafer carriers between load ports of different wafer processing or other tools during the semiconductor fabrication process. The wafer carriers include standard mechanical interface (SMIF) pods which can hold a plurality of wafers (e.g. 200 mm or 8 inch), or front opening unified pods (FOUPs) which can hold larger 300 mm (12 inch) or 450 mm (18 inch) wafers. In general, a wafer carrier is designed to hold at least one wafer. More specifically, the wafer carrier may comprise a plurality of slots each of which can hold one wafer. Typically, a wafer carrier holds on the order of approximately 25 wafers.
An overhead hoist transfer (OHT) system is commonly used to transport wafer carriers, such as FOUPs or SMIFs, from the load port of one tool to the load port of the next tool in the processing sequence. A wafer carrier transported by an OHT transfer system typically has a door during the transfer process for production quality control, e.g. to seal the wafer carrier against entry of external contaminants to keep wafers inside the wafer carrier clean, and/or to protect the wafers from falling off the wafer carrier.
Due to repetitive usage and transportation, a wafer carrier may have quality defects or even catastrophic failures, which will impact quality of wafers held inside the wafer carrier. For example, a wafer carrier may have a broken tenon, a worn out mini-contact, a defect on a latch key groove or a filter. There is no existing tool for inspecting a wafer carrier to detect these wafer carrier defects. As such, an apparatus and method for inspecting wafer carriers is desired.